1. Field of Inventions
The present inventions relate generally to the treatment of the heart and, more particularly to treatments that, among other things, stimulate angiogenesis and relieve angina.
2. Description of the Related Art
Atherosclerosis, which is a leading causes of death, occurs when plaque develops at various locations within the arterial system, thereby restricting the flow of blood through the affected vessels. When atherosclerosis occurs within the blood vessels that supply blood to the muscles of the heart, myocardial infarctions, ischemia and/or angina can result due to the reduction in blood flow.
A variety of myocardial revascularization techniques have been developed in recent years in an attempt to increase the flow of blood into the heart muscle and to stimulate angiogenesis, i.e. the creation of new blood vessels within the heart muscle. In percutaneous myocardial revascularization (PMR), which is also referred to as direct myocardial revascularization (DMR), channels are formed in the endocardial surface with catheter-based devices. The PMR and DMR channels extend partially through the ventricular wall. Transmyocardial revascularization (TMR), on the other hand, involves the formation of channels that extend completely through the ventricular wall. Although the use of mechanical piercing and cutting devices has been proposed, the revascularization channels are typically formed with a laser device or the combination of mechanical and laser devices. Radiofrequency energy delivered through an electrode has also been used to create craters on the endocardial surface.
Although they have proven to be useful, the inventor herein has determined that there are a number of shortcomings associated with conventional myocardial revascularization techniques. For example, the creation of channels through the ventricular wall during TMR is a relatively time consuming procedure and additional time is required to stop the bleeding associated with the procedure. A single channel takes about three to five seconds to create and pressure must be applied to the channel (usually with a finger) for one to two minutes in order to give the blood time to clot and stop the bleeding. The TMR procedure also requires a relatively invasive muscle-sparing thoracotomy to access the heart and results in measurable blood loss (typically about 200–300 cc). Moreover, the pulse or continuous wave energy applied to the tissue during laser-based PMR, DMR or TMR can entrain the patient's heart rhythm and cause fibrillation or tachycardia.
Cardiac denervation, which provides relief from angina pain, is a beneficial side effect of the aforementioned myocardial revascularization techniques. Patients experience pain relief because some of the nervous tissue in the ventricular wall is destroyed during the channel formation process. The present inventor has, however, determined that the level of cardiac denervation achieved by conventional myocardial revascularization techniques is susceptible to improvement. For example, the cross-sectional area of the channels is relatively small, which limits the volume of nervous tissue that is destroyed by the channels. PMR and DMR techniques are further hampered by the fact that the nervous tissue is concentrated close to the epicardial surface. PMR and DMR channels, which extend through the endocardial surface and only partially through the ventricular wall, fail to reach the region closer to the epicardial surface that contains the higher concentration of nervous tissue.